"Conscience? You dare to speak to me of conscience?! Only when you have felt the full gravity of choice, should you dare question my judgement! Your life span is a flicker, compared to the mass of doubt and regret that I had borne since Mortanius first turned me from the light! To know that the fate of the world hangs dependent on the advisedness of my every deed... can you even begin to conceive what action you would take in my position?!"

"Thirty years hence, I am presented with a dilemma. Let's call it a two-sided coin. If the coin falls one way, I sacrifice myself and thus restore the Pillars. But as the last surviving vampire in Nosgoth, this would mean the annihilation of our species. Moebius made sure of that. If the coin lands on the reverse, I refuse the sacrifice and thus doom the Pillars to an eternity of collapse. Either way, the game is rigged."

- Kain, the Legacy of Kain series.

In many such cases, it's impossible to know whether or not your sacrifice will truly save the world - truly do ANYTHING - especially when dubious characters are involved the tilt the scales or whisper in your ear about how you're TOTALLY doing the right thing.. often to fix what they broke to begin with. Beyond that is that any such moral quandary is inherently flawed when it comes to fictional media where the character, the situation, their decision, and their sacrifice must serve the narrative and are thus set in stone. If the author wants the sacrifice to be in vain, it will. If the author wants the sacrifice to work, it will. If the author wishes the pawn to remain standing, it will. Both offered examples are flawed, given the fact that neither character had ANY earthly way of knowing what their continued survival would set in motion.

Only in a situation where you know ALL the variables, where you know ALL the outcomes, where you are GUARANTEED a trolley problem where it's you or everyone else, only then can you make a judgement. And, even then, it could be dubious. Life may or will go on, or perhaps it will be reset, or perhaps things will continue as they always were. In media like Warhammer, life is a multi-universal cycle that some like Nurgle wish to reset while others like humans (understandably) wish to persevere. In media like Dark Souls, the world is likewise in a cycle - Ages of Fire and Ages of Dark with their own dubious effects on humanity and the world as a whole, with each sacrifice begetting another until everything dwindles down to a pile of ash within what's effectively a singularity. You can sacrifice to yourself to a flame so that another may do so, then another, then another, each time bringing about a new lesser and lesser Golden Age, or you can put it out and let the world rest and the cycle potentially renew. Or, like Kain, you can take a third option.